A transmission of the type here envisaged comprises a hydrostatic pump fluidically linked with a hydrostatic motor whose sense of rotation can be varied by changing the position of a tiltable control plate within the pump. When the tilt angle of this plate is zero, i.e. when the plate is perpendicular to the axis of rotation, the motor is positively arrested.
The continuous adjustability of hydrostatic transmissions from high forward torques through standstill to high reverse torques, at speeds determined by that of a prime mover driving the pump, makes such transmissions eminently suitable for use in forklift trucks and similar vehicles designed for the transportation of heavy cargoes across factory yards or warehouse floors.
When the driver of a loaded vehicle of this type reverses a shift lever to change direction while the vehicle is moving at high speed, the cargo is liable to slide off its fork, platform or other support as the vehicle comes sharply to a stop before reversing its course. In order to prevent such mishaps, it has already been proposed to displace the control plate of the engine-driven hydrostatic pump with the aid of a switchover piston in an ancillary cylinder which is hydraulically shifted into either of two operating positions under the control of a selector lever by way of throttled conduits preventing rapid reversals. Reference may be made in this connection to an article by F. S. Glaser and H. Nikolaus, entitled "Auslegung hydrostatischer Fahrantriebe fuer Arbeitsmaschinen", published in the periodical "Oelhydraulik und Pneumatik", 1973, No. 3; see especially FIG. 22 of that article. The throttling of the oil flow in such a control system minimizes the risk of significant cargo shifts on the vehicle but delays the buildup of sufficient pressure from the engine-driven pump to accelerate the vehicle in the opposite direction.